1. Field of the Invention
This invention relates to a method of inserting optical fibers into spiral grooves provided in a spacer in the production of a spacer type optical fiber cable.
2. Description of the Related Art
FIG. 4 shows an example of a spacer type optical fiber cable. In this type of cable 1 four spiral grooves 4a, 4b, 4c and 4d are formed in the peripheral surface of a spacer 3 having an anti-tension member 2 at its center. The spiral grooves 4a, 4b, 4c and 4d extend longitudinally along the spacer 3 with a predetermined pitch. Optical fibers 5a, 5b 5c and 5d are provided in grooves 4a, 4b, 4c and 4d.
A production line for producing the spacer type optical fiber cable 1 will now be described with reference to the schematic illustration in FIG. 5. The spacer is drawn out from a supply bobbin I and to the right by means of a drawing capstan III. The optical fibers 5a, 5b, 5c and 5d are inserted into the spiral grooves 4a, 4b, 4c and 4d of the spacer 3 by means of an optical fiber gathering device II (described in detail below). The spacer 3 is then wound onto a winding bobbin IV through the drawing capstan III. The supply bobbin I, the drawing capstan III, and the winding bobbin IV all rotate in the same direction at a certain speed by means of a main motor (not shown). The optical fibers 5a through 5d are spirally inserted into the grooves 4a through 4d of the spacer 3 by the effect of the rotation, respectively.
The optical fiber cable gathering device II will now be described with reference to FIG. 6. The device includes stationary lay plates 7 and 8 arranged in series with a space therebetween. These lay plates 7 and 8 have spacer inserting holes 7a and 8a formed in the center thereof, respectively. The spacer 3 is inserted into the spacer inserting holes 7a and 8a and is moved to the right (in the direction indicated by arrow A) as it is being rotated. Hereinafter, movement will be described as upstream or downstream with respect to this moving direction A. Four groove pins 10 in the form of projections are provided in the inner peripheral surface of the lay plate 7. The tips of the groove pins 10 are in the grooves 4a through 4d, thereby allowing the optical fibers 5a through 5d to be positively disposed in these grooves. Further, each of the lay plates 7 and 8 has four fiber guide holes 7b and 8b, respectively. The optical fibers 5a, 5b, 5c and 5d supplied from respective reels 9a, 9b, 9c and 9d pass through these fiber guide holes 7b and 8b and are inserted into the grooves 4a, 4b, 4c and 4d at a point downstream of the lay plate 7.
The pitch of the spiral grooves 4a through 4d provided in the spacer 3 is not always constant since variations are involved to some degree during the production process. Thus, it is necessary to measure the groove pitch P in order to correct any deviation from the preset groove pitch. Accordingly, a spiral groove position detecting device VI is conventionally provided on the upstream side of the optical fiber gathering device II, as shown in FIG. 6.
The spiral groove position detecting device VI is composed of an angle detection gear 11 and a potentiometer 12. The angle detection gear 11 is provided in a housing 13 in such a manner that it can rotate around the spacer 3 and has a groove detection pin 14 provided in the inner peripheral surface of the angle detection gear 11. This groove detection pin 14 is inserted into the spiral groove 4a in such a manner that the angle detection gear 11 is rotated in accordance with the positional deviation of the groove 4a around the axis of spacer 3. The potentiometer 13 outputs a pin position signal with a magnitude corresponding to the rotation angle of the angle detection gear 11. The deviation in rotation angle is calculated based upon this signal by an arithmetic unit (CPU). A capstan motor M of the capstan III shown in FIG. 5 is controlled in accordance with the result of this calculation.
While the detecting device VI can compensate somewhat for deviations in pitch, this conventional device has a low control accuracy. More particularly, as noted above, the groove pins 10 provided in the stationary lay plate 7 of the optical fiber gathering device II are disposed in the spiral grooves 4a through 4d so as to abut against the same. The reaction force generated by this abutment exerts a torsional force on the spacer 3, thereby damaging the spacer 3. This contributes to the low control accuracy. However, because the groove position detecting device VI is spaced from and upstream of gathering device II, detecting device VI cannot accommodate for the inaccuracy caused by the torsional force generated by the gathering device II, being capable only of measuring the rotational angle to detect deviations in pitch.